DC is a reverse-polish desk calculator
which supports unlimited precision arithmetic.
It also allows you to define and call macros.
Normally DC reads from the standard input;
if any command arguments are given to it, they are filenames,
and DC reads and executes the contents of the files
instead of reading from standard input.
All normal output is to standard output;
all error messages are written to standard error.

To exit, use `q'.
C-c does not exit;
it is used to abort macros that are looping, etc.
(Currently this is not true; C-c does exit.)

A reverse-polish calculator stores numbers on a stack.
Entering a number pushes it on the stack.
Arithmetic operations pop arguments off the stack and push the results.

To enter a number in DC, type the digits,
with an optional decimal point.
Exponential notation is not supported.
To enter a negative number, begin the number with `_'.
`-' cannot be used for this, as it is a binary operator
for subtraction instead.
To enter two numbers in succession,
separate them with spaces or newlines.
These have no meaning as commands.